Nov., 1921
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
1043
The Effect of Varying Hydrogen-Ion Concentration upon the Decolorization of Cane Juice with Carbon' By Joseph F. Brewster and William G. Rakes, Jr. BUREAUOB CHEMISTRY, UNITEDSTATESDEPARTMENT OF AGRICULTURE, WASHINGTON, D. C., AND THE LOUISIANA SUGAREXPERIMENT STATION, NEW ORLEANS, LOUISIANA
t
It has been pointed out by Wijnberg2 that better decolorization of sugarcane juice may be obtained with Norit if the juice is rendered slightly acid. An acidity of 0.01 N is recommended, but what acid is to be used is not stated. Wijnberg further states that a t 0 . 2 N to 0 . 3 3 N alkalinity decolorization with Norit sinks nearly to zero. Furthermore, Norit that has become saturated with the coloring matter of cane juice may be revivified to nearly its original activity by boiling with dilute alkali, whereby the coloring matters are dissolved. The same author states that the pectins of cane juice are more readily adsorbed by Norit when the medium is slightly acid, and explains this action on colloid chemical grounds. Further scientific explanation of this effect of acid in facilitating the decolorizing action of carbons is to be found in previous work in colloid chemistry. Perrin3 states that the size of the particles of a colloid is a function of the reaction of the medium. Mayer, Schaeffer and Terroine4 conclude that, in a very general manner, the addition of traces of acids to the solution of a negative colloid and of alkali to the solution of a positive colloid has the effect of increasing the size of the colloid particles. The addition of alkali to the first and of acid to the second produces the reverse. As examples, those authors state that Congo red, which is positive, becomes blue on the addition of acid, and a t the same time the colloidal particles disappear. I n suspensions of the phthaleins, which are negative colloids, addition of alkali renders them red and limpid. The same applies to suspensions of alkaloids, proteins, soaps, etc. Holderer6 found that the invertase of Aspergillus niger entirely passed through a porous clay filter when its solutions were neutral to phenolphthalein. When neutral to methyl orange the invertase was almost completely retained. Holderer states that the extraction of invertase from the mold is facilitated by making the water of maceration slightly alkaline. There can be little doubt that the colloids and coloring matters of cane juice and sugar-house products are affected by acids and alkalies in a manner similar to the examples just cited, and it is very probable that these effects are produced by the concentration of hydrogen or hydroxyl ions in the medium. Believing that the determination of H-ion concentration might find some important applications in the various processes of cane-juice clarification, the writers have done some preliminary work, the results of which are in part reported here. It is hoped that this may be continued and extended and a fuller report published. In the course of experiments a t the Louisiana Sugar Experiment Station in November and December 1920, the H-ion concentrations of many lots of normal cane juice were determined. The pH values found ranged from 4 . 8 to 5 . 8 . These values seemed to have very little relation to the titratable acidity as it is usually determined. One lot of juice titrated 1 . 4 3 cc. 0.1 N per 10 cc. and had a p H value of 4 . 8 . 1 Presented before the Section of Sugar Chemistry and Technology at the 6lst Meeting of the American Chemical Society, Rochester, N. Y., April 26 to 29, 1921. * I n t e r n . Sugar J., 1 7 (1915), 70. a J. chim Bhys., 1904-05. @ Compf. rend., 145 (1907), 918. Ibid., 149 (1909), 1153.
Another titrated 2 cc. 0 . 1 AT and had a p H value of 5 . 0 . The juice with the lower titratable acidity showed a slightly higher H-ion concentration. The acids of normal cane juice are organic acids little dissociated, so that slight increase or decrease of the quantities of these present would appear to have little effect on the p H value. I n the caseof abnormal cane, however, referring particularly to fermented cane, increase in H-ion concentration of the juice is to be expected as a result of the formation by organisms of stronger acids than those existing in normal cane. EXPERIMENTAL PART For the determination of H-ion concentrations of cane juice, the spot test was found more accurate and more rapid than any other colorimetric method. The indicators and buffer mixtures recommended by Clark and Ilubsl were used, the buffer mixtures being checked withthe potentiometer. Fresh cane juice was expressed with the laboratory mill and clarified with kieselguhr. The juice, in 200-cc. portions, was acidified with 10 per cent acetic acid to thedesiredpH value, and the volume was adjusted to 220 cc. For neutralizing and for obtaining alkalinity N sodium hydroxide was used. For the decolorization tests, the 220 cc. of juice with pH value adjusted were treated with 2 g. of decolorizing carbon, brought to boiling, and filtered. When the liquid was cooled to room temperature the colorimetric readings were made with the Hess-Ives tintphotometer, and the color units and totals were determined from the table of Meade and Harris.2 The results shown in Table I were obtained by the use of different carbons. Color units left in the juice, as derived from Meade and Harris table, and total units divided by 3 are shown. The first set of figures were obtained in media weakly alkaline, neutral, and a t two different degrees of acidity, respectively. The remaining figures were all obtained at varying acidities, from pH = 4 t o about pH = 5. For comparison there are included colorimetric readings on the juice untreated with carbon. TABLEI oH=8 Color Redscreen 23.4 A {Green screen 44.4 Units Bluescreen 73.0 Total units 46.9 3
B
oH=7 8.3 24.7 46.0
28.07
pH = 4 . 1 pH = 4 . 4 pH ~ 4 . 11.8 Red screen 8.3 16.2 {Green screen 1 9 . 8 32.6 29.9 Units Bluescreen 3 5 . 6 35.5 50.8 Total units 21.2 26.6 32.3 3 Color
pH -4.16 Red screen 7.2 Green screen 15.0 C Units Blue screen 24.7 Total units 15.6 3 Color
D
24.12
Juice Untreated with o H = 5 . 4 D H - ~ Carbon 18.6 11.6 57.7 27.3 22.2 104.4 46.0 29.9 165.0
(
Color
Red screen 9.4 Green screen 18.6 Units Blue screen 28.6 Total units 18.9 3 1
J. Bact., 2 (1917), 1. THIS JOURNAL, 12 (1920),688.
21.2
109.0
Juice Untreated with 5 p H ~ 4pH . 7- 4 . 8 Carbon 19.8 21.0 54.2 31.2 32.6 98.9 54.2 57.7 150.6 35.1
pH = 4 . 3 2 9.4 17.4 24.7
37.1
101.2
pH - 4 . 9 2 11.6 21.0 28.6
17.2
20.4
15.0 26.0 32.6
15.0 32.6 29.9
24.5
25.8
1044
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMIST&Y
It is interesting to note under A that less total color was left a t pH = 7 (neutrality) than a t pH = 5.4,the natural acidity of the juice. The rest of the figures demonstrate clearly that increase of H-ion concentration brings about increase of decolorization. These results may be duplicated by using phosphoric in the place of acetic acid. I n this connection, when working with increase of H-ion concentration in sucrose solutions it is necessary to take into consideration the fact that the rate of inversion of sucrose increases in proportion to increase in the concantration of hydrogen ion. The extent of inversion was determined a t several p H values used in the decolorization tests. The results shown in Table I1 were obtained by boiling 200 cc. of juice under reflux after the H-ion concentration had been adjusted to the desired point by addition of acetic acid. The time factor for these inversions differs entirely from that of the decolorization tests, the experiments being made in the manner described more to accentuate the differences in rate of inversion with increase in p H value than to imitate the conditions of the decolorization experiments. At the end of 2 hrs.' boiling the juice was cooled, aliquot parts were taken, and the direct polarization was read after clarification with lead acetate. I n Table I1 are shown the H-ion concentration, the direct polarization after 2 hrs.' boiling, and the direct polarization of the original juice. This was 8.9" V. From these data were calculated tho percentages indicated. The sample
Vol. 13, No. 11
described in the first column under pH = 5 WRS the original juice without addition of acid. The loss of direct rotation here wap 3 . 4 per cent of the original. TABLE11-INVERSION OF SUCROSE Original Pokri4 p H - 4 zation Direct polar- P H - 5 pH=4.8 p H = 4 6 pH ~ 4 . pH=4.2 ization ... 8.6 Polarization per cent of origin$ 96.6 Percentloss 3.4
.
8.5
7.0
6.5
6.6
5.0
8.9
95.5 4.5
78.6 21.4
73.0 27.0
74.2 25.8
56.2 43.5
... ...
In view of the amount of inversion that can be brought about even a t an acidity as low as pH = 5, about that of normal juice, it would appear to be somewhat doubtful that much advantage would be gained in practice by acidifying to improve decolorization unless conditions were very carefully controlled. Since fairly high acidity and a temperature a t or near the boiling point of the juice are required for best results, the third factor to be controlled is that of time of exposure to high acidity. The authors have obtained good results by heating the juice mixed with carbon to the boiling point, adding phosphoric acid to an acidity of pH = 4, allowing a short time for action, and neutralizing back with milk of lime. Calcium phosphate precipitates out and is removed with the carbon by filtration. One must be careful not to over-lime the mixt,ure and thus obtain an alkaline reaction. It is safe to stop the addition of lime a t about p H = 6 . 5 . By this procedure as good decolorization may be obtained as by carrying through the entire procedure a t p H = 4.
The Iodine Numbers of Unsaturated Hydrocarbons and Cracked Gasolines' By W. F. Faragher, W. A. Gruse and F. H. Gamer M E L ~ OINSTITUTE N OF INDUSTRIAL RESEARCH, PITTSBURGH, PENNSYLVANIA
The work here presented represents an att,empt to clear up, in small part, a t least, the uncertainties connected with the determination of the unsaturated constituents of cracked gasolines, and, if possible, to find the conditions under which unsaturation may be determined accurately. Such data are of interest, not only from the point of view of the derivatives obtainable, but also from that of the keeping qualitties of a gasoline itself. The methods ordinarily employed for this determination are, in the order of the frequency of their use, the sulfuric acid absorption method, the iodine number method, and the bromine absorption method. The sulfuric acid absorption method is the one most generally used, but it is practically useless from the standpoint of information obtainable, since sulfonation, polymerization, solution, and possibly oxidation occur along with the absorption of unsaturated compounds. The method has been standardized by Dean.2 The bromine absorption methodS is least employed because of its inconvenience, and it is useful chiefly when it is desirable to determine substitution as well as addition. The iodine number method is well known, chiefly in the field of animal and vegetable fats and oils. The literature on its use for mineral oils is scanty; for gasolines, the method has been standardized by Dean,2 who was interested in getting a rapid and reproducible technique. The results obtained were found to depend entirely upon uniform procedure. Dean used the Hanus solution, a 30-min. reaction period, and a quantity of gasoline so chosen (depending on its unsaturation) that from 10 to 30 per cent of the reagent was absorbed. The weight of the gasoline varied from 0.04 to 0.20 g. 1 Presented before the Petroleum Section at the 61st Meeting of the American Chemical Society, Rochester, N. Y.,April 26 to 29, 1921. a Bureau of Mines, Techni'al Paper 181. 8 McIlhiney, J . A m . Chem. Soc., 21 (1899), 1084;Schxeitzer and Lungewitz, J . .Tot. Chem. I n d . , 14 (1895), 130.
Smith and Tuttlel have determined iodine values of lubricating oils, using the Hanus solution and a 30-min. period of reaction. They believed it advisable to use as much as 1 g. of oil. This procedure gave a nearly constant value with slight variations in quantity of sample, but very low iodine numbers. Radcliff e and Polychronis2 have studied the action of Hubl, Hanus, and Wijs solutions on heavy mineral oils. They found that the numbers obtained were in the order Hanus > Wijs > Hubl, though the Hanus and Wijs values agreed fairly closely. All three solutions gave increasing values over a 24-hr. period, and the character of the curves for the three solutions was about the same. Radcliffe and Polychronis discarded the Hanus solution because, in the first place, a difference of 20" C. in temperature caused a variation of 5 units in an iodine number of 30, and because they found that the presence of a slight excess of bromine produced a considerable change in the iodine number of an oil determined. The Hubl solution gave an iodine number much below the theoretical value for an amylene a t the end of 2 hrs., while the Wijs solution gave a satisfactory number. Roderer3 has found that for heavy fractions of mineral and lignite tar oils the Hubl-Waller and Wijs solutions give maximum values, using five- to ten-fold excess of reagent and periods of 16 to 2 1 hrs. Grun and Ulberich,4 working with heavy fractions of lignite tar oils and using the Wijs reagent, found iodine numbers higher than the olefine content, as estimated by other reactions, would allow. They, therefore, took the bromine absorption and substitution numbers by the method of McIlhiney and found that the Wijs solution might give 1
Buseau of Standards, Technologzc Paper
2
J . SOG.Chem. I d . , 85 (1916). 341. Z angew. Chem., 88 (19201, 235. I b i d . , 38 (19201, I, 295.
8 4
87.
